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Old Jun 14, 2008, 04:33 PM
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United States, WA, Hoodsport
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Saito 4-Stroke Valve/Tappet Gap Adjustment

Greetings All,

The Saito small to medium (FA-30 to FA-125) manual indicates valve/tappet gap adjustment in a range of .03 mm to .10 min (.002" - .004"). I am wondering what experience you all have had with valve/tappet gap settings. Is there an advantage to a wider gap or more narrow gap?

Thanks!

EJWash
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Old Jun 14, 2008, 05:43 PM
Gentle 'Bella'
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Augusta, KS USA
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Quote:
Originally Posted by EJWash1
Greetings All,

The Saito small to medium (FA-30 to FA-125) manual indicates valve/tappet gap adjustment in a range of .03 mm to .10 min (.002" - .004"). I am wondering what experience you all have had with valve/tappet gap settings. Is there an advantage to a wider gap or more narrow gap?

Thanks!

EJWash
EJW - Edge toward the narrower gap.

Wider gaps allow the valve to remain on the seat longer thus cooling it. This is more practical for gasoline fired motors and allows for some clearance deviation due to expansion of parts due to heat. In a glow motor, combustion temps are lower, expansion is less of an issue, and importantly the rocker/valve contact points are less likely to get hammered and peened with the tighter clearance. The designers factor in clearances for optimum valve timing and I'm guessing they'd go for the tighter clearances too plus this allows for some wear in of the parts but still stay in specs.
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Old Jun 15, 2008, 08:19 AM
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United States, TX, Weatherford
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Open duration can effect your over all timing. By staying within the specs the engine will operate best. To tight and perfromance drops off, to lose, and perfromance drops off plus other things happen like push rods get hammered. So stay with in the go no go range given.

Cheers,

Chip
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Old Jun 15, 2008, 11:38 AM
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Thanks Chip,

I guess I should have made it clear that I was looking for experience *within* the engine manufacturerís (Saito) valve/tappet adjustment range of .03 mm to .10 min (.002" - .004").

We have some very talented and knowledgeable modelers on this forum that have been more than willing to share their experience with us.I think itís great that we have them at our disposal.

I realize that we are not talking about a huge spread here. Only a difference of .07 mm.I just measured a single sheet of 20lb. copy paper and it is .10 mm thick, the same as the top end of the valve/tappet adjustment range. But, we are talking about a very small engine here.

I just read the OS 91 manual, and OS prints a valve/tappet adjustment range of .04 mm to .10 min (.0015" - .004"). OS does go into greater detail on how to evaluate if valve/tappet adjustment is necessary depending on the present gap. The OS adjustment procedure has you readjust the gap setting to .04 mm. Iíll go with .04 on the Saito, since this is within the allowable range, and see what the results are.

EJWash
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